Controlling Method, Power Supply, Power Controller, and Power Controlling Method

ABSTRACT

A power supply has an inductor and determines loading state of the power supply according to a compensation signal. When the loading state is determined to be a light loading state or a no-loading state, a switch is operated at a low operating frequency. When the loading state is determined to be a heavy loading state, the switch is operated at a high operating frequency. If the compensation signal exceeds a critical value, it is determined that the loading state is an overloaded state. When the overloaded state continues past a tolerable duration, the switch is turned off. The tolerable duration is determined by an external capacitor and is independent of the operating frequency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to an overloading limitation of aswitched-mode power supply (SMPS).

2. Description of the Prior Art

A power supply is a kind of power management device that transformspower from a power source to provide transformed power to an electronicdevice or component. FIG. 1 illustrates conventional power supply 60,which employs a flyback topology. In FIG. 1, bridge rectifier 62 isutilized for rectifying AC power V_(AC) to provide input power V_(IN) totransformer 64. When switch 72 is close-circuited, primary winding L_(P)of transformer 64 is charged. When switch 72 is open-circuited,secondary winding L_(s) of transformer 64 discharges to load capacitor69 via rectifier 66 to generate output power V_(OUT). Error amplifier EAcompares voltage levels of output power V_(OUT) and target voltageV_(TARGET) to generate a compensation signal V_(COM). Controller 74controls switch 72 with the aid of control signal V_(GATE) according toboth compensation signal V_(COM) and current detection signal V_(CS),which correspond to inductive current flowing through primary windingL_(P).

Many types of protection may be added to power supply 60, includingover-voltage protection (OVP), over-temperature protection (OTP), andoverload protection (OLP). Overload protection is used when outputcurrent loading of power supply 60 is too high, and when the powersupply provides power exceeding a predetermined output power level.

Overload protection may be implemented by limiting output current, or bylimiting the inductive current flowing through primary winding L_(P).Both implementations are intended to prevent power outputted by thepower supply from exceeding a certain level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional power supply acquiring a flybacktopology.

FIG. 2 illustrates a power supply according to an embodiment of thepresent invention.

FIG. 3 illustrates part of the controller and the external capacitorshown in FIG. 2.

FIG. 4 illustrates a correspondence between the operating frequencygenerated by the clock generator and the compensation signal.

DETAILED DESCRIPTION

Please refer to FIG. 2, which illustrates power supply 90 according toan embodiment of the present invention. Similar reference numerals areused in FIG. 1 and FIG. 2 to indicate same elements, same devices, orsame signals, and are not described repeatedly for brevity. Embodimentsgenerated by using elements the same as or similar to elements shown inFIG. 1 should be regarded as embodiments of the present invention. Scopeof the present invention should also follow claims of the presentinvention.

In an embodiment, controller 73 shown in FIG. 2 is implemented by asingle integrated circuit. In another embodiment, controller 73 andswitch 72 are implemented in a single integrated circuit. A differencebetween controllers 73 and 74 lies in addition of pin CT of controller73 shown in FIG. 2, where controller 73 is coupled to external capacitor75 via pin CT.

FIG. 3 illustrates part of controller 73 and external capacitor 75 shownin FIG. 2. Comparator 82 is utilized for providing over-currentprotection, and is a peak limiter for preventing any peak of currentdetection signal V_(CS) from exceeding voltage V_(CS -LIMIT). A peak ofthe inductive current flowing through the primary winding L_(P) is alsoprevented from exceeding peak current I_(CS) _(—) _(LIMIT)V_(CS-LIMIT)/R_(CS)), where R_(CS) indicates resistance of resistor CS.Comparator 84 controls an approximate peak of the inductive currentflowing through primary winding L_(P) according to compensation signalV_(COM). Voltage level of compensation signal V_(COM) corresponds topower required for sustaining a current output voltage or a loadingstate related to the current output voltage. Compensation signal V_(COM)also determines output operating frequency of clock generator 96, i.e.operating frequency of switch 72 shown in FIG. 2. For example, a lowvoltage level of compensation signal V_(COM) indicates a light loadingstate or a no-loading state, so that a corresponding operating frequencymay be equal to 20 kHz. A high voltage level of compensation signalV_(COM) indicates a heavy loading state, so that a correspondingoperating frequency may be equal to 65 kHz. The heavy loading state, thelight loading state, and the no-loading state are all regarded as normalloading states.

Current supplier 85 provides a charge/discharge current to externalcapacitor 75 via pin CT. A combination of current supplier 85 andexternal capacitor 75 may be regarded as a clock oscillator, i.e.forming a clock oscillator. When the compensation signal V_(COM) ishigher than critical voltage V_(OLP) for overload protection, i.e. whenan overload event occurs, power supply 90 is determined to beginoperating in an overloaded state, and comparator 88 starts counter 92counting according to a clock signal outputted by the clock oscillator.Once comparator 94 determines that the output of counter 92 fulfills apredetermined condition, indicating the overload event has continuedpast a tolerable duration, comparator 94 begins outputting an overloadlimiting signal for triggering overload protection, and logic controlunit 86 keeps switch 72 turned off to stop power transformation andpower transmission. If the compensation signal V_(COM) drops below thecritical voltage V_(OLP) before the tolerable duration is exceeded, i.e.when power supply 90 leaves the overloaded state, counter 92 is reset,and switch 72 continues to be operated at the operating frequencyprovided by clock generator 96. A combination of current provider 85,comparator 88, counter 92, and comparator 94 may be regarded as anoverload limiter. In another embodiment of the present invention,comparator 94 is omitted, and whether to trigger overload protection ornot is determined directly according to an output bit having value oflogical 0 or logical 1.

It can be seen from the illustration of controller 73 shown in FIG. 3that the tolerable duration indicates a maximum duration tolerable forpower supply 90 to be in the overloaded state, where the tolerableduration is determined according to both the frequency provided by theclock oscillator, which includes at least current provider 85 andexternal capacitor 75, and a predetermined condition defined bycomparator 94. The tolerable duration is independent of variation of theoperating frequency generated by clock generator 96. For example, indesign, comparator 94 is built in an integrated circuit so that externalfactors cannot change settings of comparator 94, and the frequency ofthe clock oscillator can be determined according to capacitance ofexternal capacitor 75. Therefore, the tolerable duration can be easilyadjusted by selecting an appropriate capacitance for external capacitor75.

In one embodiment of the present invention, after overload protection istriggered, overload protection is de-asserted once compensation signalV_(COM) drops below critical voltage VOLP, so that power transformationand power transmission are restored. In another embodiment of thepresent invention, overload protection is de-asserted only when the ACpower source of controller 73 is removed and restarted.

FIG. 4 illustrates a correspondence between the operating frequencygenerated by clock generator 96 and the compensation signal V_(COM).When the voltage level of compensation signal V_(COM) reaches voltageV_(CS-LIMIT), i.e. when heavy loading occurs, the operating frequency isadjusted to be heavy-loading frequency f_(HEAVY), which may be 65 kHz inone embodiment of the present invention. When the voltage level ofcompensation signal V_(COM) reaches critical voltage V_(OLP) foroverload protection, i.e. when the overloaded state is triggered, theoperating frequency is adjusted to be overloaded frequency f_(OverLoad),which may be 130 kHz in one embodiment of the present invention. Whenthe peak of the inductive current flowing through primary winding L_(P)is roughly equal to I_(CS) _(—) _(LIMIT), the operating frequency is atleast heavy-loading frequency f_(HEAVY). During the tolerable duration,i.e. when compensation signal V_(COM) is higher than critical voltageV_(OLP) for overload protection, the peak of the inductive current isapproximately controlled to be fixed to I_(CS) _(—) _(LIMIT), because ofthe restriction provided by comparator 82. However, the operatingfrequency is equal to overloaded frequency f_(OverLoad), instead ofheavy-loading frequency f_(HEAVY), where overloaded frequencyf_(OverLoad) is higher than heavy-loading frequency f_(HEAVY). Forexample, overloaded frequency f_(OverLoad) can be double or tripleheavy-loading frequency f_(HEAVY).

The above-mentioned embodiments of the present invention provide twoadvantages. First, transformer 64 is prevented from saturating. Thecurrent I_(CS) _(—) _(LIMIT) can be set to a maximum current before thetransformer 64 saturates. Therefore, as long as transformer 64 does notsaturate, the output power of power supply 90 can be temporarily raisedmerely by raising the operating frequency of controller 73 to theoverloaded frequency f_(OverLoad). Second, the tolerable duration can beadjusted externally. As mentioned before, the tolerable duration isindependent of the operating frequency, and is determined by the clockoscillator formed by both current supply 85 and external capacitor 75.Therefore, the tolerable duration can be determined easily byappropriately choosing the capacitance of external capacitor 75.However, if the tolerable duration is a few seconds, the clockoscillator will introduce large integrated circuit area if completelyformed by integrated circuits. Thus, use of external capacitor 75 toadjust the tolerable duration saves significant circuit layout area.

The switched-mode power supply is described for flyback topology, butthe embodiments of the present invention can also be utilized indown-converting and up-converting switched-mode power supplies.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention.

What is claimed is:
 1. A controlling method utilized in a power supplycomprising a switch and an inductive element, the controlling methodcomprising: detecting an inductive current flowing through the inductiveelement; determining the power supply under a normal loading state or anoverloaded state according to a feedback signal; controlling a peak ofthe inductive current to be smaller than or equal to a constantmagnitude and controlling the switch to be operated in a first frequencywhen the power supply is operated under the normal loading state;controlling the peak of the inductive current to be approximately theconstant magnitude and controlling the switch to be operated in a secondfrequency when the power supply is operated under the overloaded state,wherein the second frequency is higher than the first frequency;calculating a duration during which the power supply is operated underthe overloaded state; and stopping the inductive current when theduration exceeds a tolerable duration; wherein the tolerable duration isindependent of variation of the operating frequency.
 2. The controllingmethod of claim 1 further comprising: adapting the operating frequencyaccording to the feedback signal.
 3. The controlling method of claim 1further comprising: resetting a counter for calculating the durationwhen the power supply leaves the overloaded state.
 4. The controllingmethod of claim 1 further comprising: providing a clock generator togenerate the operating frequency; wherein the tolerable duration isindependent of the operating frequency.
 5. A power supply comprising: acontroller, for controlling an inductive current flowing through aninductive element, the controller comprising: a clock generator forgenerating an operating frequency; a current limiter for controlling apeak of the inductive current to be approximately a constant magnitude,wherein when the current limiter controls the peak to be approximatelythe constant magnitude, the operating frequency is lower than or equalto a first frequency; and an overloading limiter comprising: anoverloading identifier for identifying whether the power supply shouldenter an overloaded state according to a feedback signal, wherein whenthe power supply is operated in the overloaded state, the operatingfrequency is a second frequency higher than the first frequency; and acurrent supply, for providing a charging/discharging current to anexternal capacitor and for calculating a duration during which the powersupply is operated in the overloaded state; wherein when the durationexceeds a tolerable duration, the controller stops the inductivecurrent, and the tolerable duration is independent from variation of theoperating frequency.
 6. A power controller utilized for a power supplycomprising an inductive element and a switch, the power controllercomprising: a first comparator, for receiving a compensation signal anda current detection signal to control the switch, wherein the currentdetection signal corresponds to an inductive current flowing through theinductive element, the compensation signal corresponds to a loadingstate of the power supply, and the first comparator is utilized forapproximately determining a peak of the inductive current according tothe compensation signal; a clock generator, for roughly providing anoperating frequency of the switch according to the compensation signal,wherein the operating frequency is a high operating frequency when theloading state is a heavy loading state and the operating frequency is alow operating frequency when the loading state is a light loading stateor a no-loading state; and an overloading limiter, comprising acharge/discharge device coupled to an external capacitor, for detectingthe compensation signal to determine whether an overload event occurs,and for outputting an overload limiting signal to turn off the switchwhen a tolerable duration is exceeded after the overload event occurs;wherein the external capacitor and the charge/discharge device forming aclock oscillator, and the tolerable duration is determined by theexternal capacitor and independent of the clock oscillator.
 7. The powercontroller of claim 6 wherein the overloading limiter further comprises:a second comparator, for comparing the feedback signal with a criticalsignal and outputting an overload signal indicating the overload eventoccurred if the compensation signal is higher than the critical signal;and a counter coupled to the second comparator, for receiving a clocksignal and starting to count when the comparator outputs the overloadsignal; wherein the overload limiting signal is outputted after an theoverload signal outputted from the counter fulfills a condition.
 8. Thepower controller of claim 7, wherein a frequency of the clock signal isdetermined by both the external capacitor and the charge/dischargedevice, and the tolerable duration is related to both the condition andthe frequency of the clock signal.
 9. The power controller of claim 6,wherein the clock oscillator determines the operating frequency to be anoverloaded frequency higher than the high operating frequency within thetolerable duration after the occurrence of the overloading event. 10.The power controller of claim 6 further comprising: a peak limiter, fordetecting the current detection signal and outputting a peak limitingsignal to control the switch, and thereby approximately limiting thepeak of the inductive current to be a limit peak.
 11. The powercontroller of claim 10, wherein the peak of the inductive current is thelimit peak within the tolerable duration after the occurrence of theoverload event.
 12. A power controlling method utilized for a powersupply, the power supply comprising an inductive element and a switch,the power controlling method comprising: determining a loading state ofthe power supply according to a compensation signal, controlling theswitch to be operated under a high operating frequency when the loadingstate is a heavy loading state, and controlling the switch to beoperated under a low operating frequency when the loading state is alight loading state or a no-loading state; and determining the loadingstate to be an overloaded state when the compensation signal exceeds acritical value, and turning off the switch when the overloaded statelasts beyond a tolerable duration; wherein the tolerable duration isdetermined according to an external capacitor and is independent of boththe high and low operating frequencies for operating the switch.
 13. Thepower controlling method of claim 12 wherein the switch is controlled tobe operated under an overloaded frequency higher than the high operatingfrequency within the tolerable duration when the loading state is theoverloaded state.
 14. The power controlling method of claim 12 furthercomprising: detecting an inductive current flowing through the inductiveelement for generating a current detection signal; and roughlydetermining a peak of the inductive current according to both thecompensation signal and the current detection signal.
 15. The powercontrolling method of claim 14 further comprising: providing a limitsignal for limiting a peak of the inductive current to approximately bea limit peak; wherein the peak of the inductive current is limited to bethe limit peak within the tolerable duration after the compensationsignal exceeds the critical value.
 16. A power controlling methodutilized for a power supply, the power supply comprising an inductiveelement and being controlled by a switch to charge or discharge forgenerating an output power, the power controlling method comprising:providing a clock generator for roughly providing an operating frequencyof the switch; detecting a loading state of the power supply; adjustingthe operating frequency according to the loading state, wherein theoperating frequency is a first frequency when the loading state is aheavy loading state; controlling the operating frequency toapproximately be a second frequency higher than the first frequencywithin a tolerable duration when the loading state is an overloadedstate; and ceasing operations of the switch after the tolerable durationis exceeded; wherein the tolerable duration is independent of a clockoscillator.
 17. The power controlling method of claim 16 furthercomprising: providing a compensation signal according to a voltage levelof the output power; wherein detecting the loading state of the powersupply comprises: comparing the compensation signal with a criticalsignal, and determining the loading state to be the overloaded statewhen the compensation signal is higher than the critical signal.